The following invention relates to dampers and other devices which are located within ducts which control flow rates of fluids including liquids, air and other gases passing through the ducts. More particularly, this invention relates to dampers with flow rate measurement capabilities included with the damper.
Modern buildings typically have complex heating, ventilating and air conditioning systems to efficiently provide comfortable living environments within the buildings. The air handling equipment typically includes networks of ducts for transporting the appropriately conditioned air to various different locations within the building. Among the various types of equipment which are located within such air handling systems are dampers.
Dampers control the flow rate of air or other gases passing along a particular duct by adjustment of the orientation of the damper. Typically, a ventilation system will be carefully designed with the ventilation system requiring particular flow rates during particular operational modes for the system. For the ventilation system to operate according to the design, the ventilation system must receive accurate information regarding what the flow rate is through the damper and be able to precisely adjust the flow rate through movement of the damper.
In typical prior art ventilation systems, flow rate measurement is performed with equipment separate from the damper. For instance, a pitot tube can be provided upstream or downstream from a damper which measures total pressure and static pressure and compares the two pressures to calculate the flow rate of air or other gas passing through the duct. For the pitot tube flow rate sensor to perform adequately, it must be spaced sufficiently far from the damper so that turbulence, such as that particularly caused by a partially closed damper, does not alter the flow rate measurements taken by the pitot tube. Also, such pitot tubes benefit from being spaced away from elbows or other apparatus within the ducts for accurate measurements to be made. Often the duct pathways cannot conveniently provide sufficiently large straight sections for effective flow rate measurement with pitot tubes. Even when such straight sections are available, the placement of the pitot tube flow rate sensor at a location spaced from the damper requires that two separate pieces of equipment be installed within the duct. Accordingly, a need exists for a damper for controlling flow rate and which also includes a flow rate sensor therein.
U.S. Pat. No. 5,730,652 to Van Becelaere teaches a damper with a blade which has openings therein which lead to a pressure differential sensor. One opening is provided in a leading edge of the damper and one opening is provided in a trailing edge of the damper. Van Becelaere utilizes a pressure differential in much the way that a pitot tube operates to measure flow rates present adjacent the surface of the damper itself. While Van Becelaere does incorporate flow rate measurement into the damper itself, Van Becelaere is limited in that the pressure readings are taken directly adjacent the surface of the damper where flow conditions are often disrupted by the orientation of the damper and surface flow irregularities, and are thus subject to imprecision. The Van Becelaere device also requires a replacement damper and is not retrofittable onto an existing damper.
Accordingly, a need exists for a gas flow rate measurement device which can be incorporated into a damper and accurately measure a flow rate of air/gas passing through the damper. Specifically, this need exists both in dampers in air handling units and in variable air volume (VAV) boxes. An analogous need also exists for liquid flow rate measurement devices integrated into fluidic valves within liquid handling systems.
This invention provides a damper with flow rate measuring pressure sensors attached to the damper assembly but spaced away from surfaces of the blades within the damper assembly. The damper is typically configured as a damper assembly with multiple blades spanning a duct or opening. The damper can also be configured as a valve within a liquid handling system. At least one of the blades, such as the top blade, is fitted with a sensing structure extending from each of the surfaces of the blade. The blade includes a leading surface facing upstream and a trailing surface facing downstream. An axle passes through a core of the blade and is pivotably supported within the duct. A drive is coupled to the axle and can cause a position of the axle to be adjusted between a horizontal blade orientation which leaves the duct essentially unobstructed and a vertical orientation which substantially closes the duct. A position transducer is provided which measures an orientation of the blade and sends this information to an appropriate controller.
The sensing structures provide sensing holes passing thereinto on a portion of each sensing structure which is spaced away from the surfaces of the blade. The sensing holes which are located on the sensing structure attach to the leading surface of the blade most preferably face upstream when the top blade is in its horizontal totally open orientation. In contrast, the sensing holes attached to the sensing structure of the trailing surface face downstream when the blade is oriented in its horizontal totally open orientation.
The sensing holes above the leading surface of the blade encounter pressure which is at least partially due to the velocity of the air passing by the duct. The sensing holes extending from the trailing surface of the blade face at least partially downstream and are located behind the blade and so experience a pressure which does not have an appreciable velocity component. Hence, a pressure differential correlating with the flow rate exists.
The sensing holes adjacent the leading surface pass out of the assembly and on to a pressure sensor. The sensing holes adjacent the trailing surface pass out of the assembly and on to the pressure sensor. The pressure sensor typically is a differential pressure sensor which merely measures a difference in pressure between the sensing holes adjacent the leading surface and the sensing holes adjacent the trailing surface of the blade.
A controller for the damper would typically receive a signal from the pressure sensor indicative of the pressure differential which was measured. This controller would typically also include a signal from the blade position transducer indicative of the exact position of the blade. The controller would then calculate the flow rate based on the pressure differential and the particular orientation of the blade.
Because the sensing holes are located on a sensing structure spaced from the surfaces of the blade, a precise pressure differential correlating with the flow rate of the air is measured, particularly when factoring in the position of the blade at the time that the pressure differential reading was obtained. The controller can then accurately position the blades of the damper assembly in accordance with the overall ventilation system design.
Accordingly, a primary object of the present invention is to provide a damper which can both control a flow rate of air passing through a duct and measure a flow rate of air passing through the duct.
Another object of the present invention is to provide a flow rate measurement device which is positioned adjacent the blades of a flow rate control damper.
Another object of the present invention is to provide a flow rate measurement device which is coupled to a damper and which measures a position of the blades of the damper as well as a pressure differential between sensing holes on opposite sides of the damper blades.
Another object of the present invention is to provide a flow rate measurement device coupled to a damper which has maximum sensitivity when the blades of the damper assembly are open.
Another object of the present invention is to provide a flow rate measurement device which can accurately and dependably measure a flow rate of air or other gases passing through a duct adjacent a damper over long periods of time without maintenance.
Other further objects of the present invention will become apparent from a careful reading of the included drawing figures, the claims and detailed description of the invention.